Fair Value of Financial Instruments - Impaired Loans and Other Real Estate (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Collateral Dependent Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	$ 516	$ 508
Other Real Estate Owned-Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		22
Other Real Estate Owned-Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		266
Fair Value on Nonrecurring Basis [Member] | Collateral Dependent Impaired Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	516	508
Fair Value on Nonrecurring Basis [Member] | Collateral Dependent Impaired Loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total	$ 516	508
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Residential [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		22
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Residential [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		22
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Commercial [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		266
Fair Value on Nonrecurring Basis [Member] | Other Real Estate Owned-Commercial [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value on a nonrecurring basis, Total		$ 266